The present invention relates to cathode current control circuits for traveling wave tube (TWT) amplifiers, and is more particularly directed to a cathode current control circuit for providing closed-loop control to maintain the cathode current of a gridded TWT amplifier at a predetermined level.
TWT devices are typically designed for operation at optimum cathode current levels. Operation at optimum cathode current levels generally provides for increased operating lifetimes, while deviation from such optimum cathode current levels reduces operating lifetimes.
Practical financial and technical considerations limit the extent to which uniformity can be realized with respect to characteristics of electron gun assemblies, thereby resulting in the necessity of both initial and intra-life operating parameter adjustments. Throughout the useful life of a TWT, or other filamented devices, dimensional changes occur within the electron gun assembly, and reduction in the emissive properties of the base cathode material similarly occur. These changes tend to change the TWT cathode current and the output of a TWT amplifier.
As a result of the foregoing characteristics of TWT devices, adjustment of TWT operating parameters must be made upon initial installation and during the operating lifetime. Typically, such adjustments are made by human operators and are directed to changing the available grid-pulse voltage to obtain the required TWT cathode current. Adjustment by a human operator may require a certain level of skill and specialized test equipment, and provides potential for error.
The cathode current in a TWT is normally controlled in pulsed operations by the grid pulse voltage. Typical controllers used for controlling TWT cathode current are believed to require tens of milliseconds to achieve a stable TWT beam current, and require periodic refreshing (TWT beam pulsing) to retain the beam current reference and the required beam current stability. Such known controller circuits are believed to be analog in nature and used in applications where response and decay times are of lesser concern.